Diesel engines are often used to power various types of work machines. Despite various improvements made over the years to diesel engines, diesel engines still remain not only a source of vibration and noise, but also undesirable emissions, such as carbon dioxide (CO2), nitrogen oxides (NOx), unburned hydrocarbons and soot. All of these have been found to contribute to global warming and air pollution.
Over the years, engineers have attempted to decrease the use of diesel engines in order to decrease undesirable emissions, along with noise and vibrations. For instance, work machines often use a diesel engine to power a hydraulic pump that delivers hydraulic fluid to a hydraulic cylinder. Movement of a plunger within the hydraulic cylinder drives the movement of the work machine's implement, such as a loader, excavator, or the like. When the plunger is retracting in the gravity direction of a weight load, some of the energy of the hydraulic fluid being pushed from a decreasing volume of the cylinder below the plunger can be captured and re-used. The hydraulic fluid being pushed out of the cylinder can flow to an increasing volume above the retracting plunger within the cylinder. Thus, during retraction, some of the hydraulic power created within the hydraulic cylinder can be recovered, and the pump hydraulic fluid flow can be decreased, thereby decreasing the required diesel engine power.
However, because the increasing volume above the retracting plunger is limited by a rod connecting the plunger to a weight, the increasing volume is substantially smaller than the decreasing volume below the retracting plunger. In order to accommodate the smaller size of the increasing volume, a throttle valve is used to bleed to a hydraulic tank approximately 50% of the pressurized hydraulic fluid flowing from the fluid volume below the plunger. Thus, only a portion of the hydraulic fluid being pushed from the cylinder by the retracting plunger is available to produce power within the power system. Because of the significant amount of high pressure hydraulic flow being bled from the power system, the rate of energy recovery can be too low to be efficient. In addition, the energy recovery only occurs when the plunger is retracting within the cylinder, thereby further reducing the efficiency of the energy recovery.
In order to increase the energy recovery, engineers have found methods of storing the captured energy from the pressurized hydraulic flow. For instance, Patent Abstracts of Japan 2002-195218, which was published Jul. 10, 2002, shows that during plunger retraction, the flow of hydraulic fluid from the hydraulic cylinder can also be used to rotate a turbine that powers a generator. Electric current generated by the generator is delivered to a water reservoir, in which electrolysis separates the water into hydrogen and oxygen. The hydrogen is accumulated and stored in a hydrogen absorbing alloy. When needed, the hydrogen gas can be delivered to a fuel cell, in which it is re-combined with oxygen to produce heated water and electric current. The electric current is delivered to an electric motor that powers the hydraulic pump. Thus, the diesel engine can be replaced with the electric motor partially driven by hydraulic power, thereby even further reducing undesirable emissions, noise, and vibrations, and increasing the efficiency of the energy recovery.
Although the electric motor powered by the fuel cell does decrease undesirable emissions, noise and vibrations, there is still room for improvement. Even with the use of the electric motor, the excess hydraulic flow from the fluid volume below the retracting plunger to the fluid tank is throttled by the throttle valve prior to powering the turbine. Thus, some of the hydraulic power of the flow is wasted, rather than used to power the generator.
The present invention is directed to overcoming one or more of the problems set forth above.